Azeotropic mixture



April 7, 1970 K, P, MURPHY ET AL 3,505,232

AZEOTROPIC MIXTURE Filed Jan.

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INVENTORS KEVIN P. MURPHY SABATINO R.ORFEO )www Q Qwd;

A TTORNEY United States Patent O 3,505,232 AZEOTRUPIC MIXTURE Kevin PaulMurphy, Bernardsville, and Sabatino R. Orfeo,

Morris Plains, NJ., assignors to Allied Chemical Corporation, New York,N.Y., a corporation of New York Filed Jan. 9, 1967, Ser. No. 607,922Int. Cl. (109k 3/02 U.S. Cl. 252-67 6 Claims ABSTRACT F THE DISCLOSURE Alow boiling azeotropic composition consisting essentially of a mixtureof monochloromonouoromethane and dichlorotetrafluoroethane, useful as arefrigerant, heat transfer medium, gaseous dielectric and as workingfluid in a power cycle.

This invention relates to iiuorinated hydrocarbons, and moreparticularly to constant boiling iiuorocarbon mixtures, which comprisemonochloromonofluoromethane and dichlorotetrajuoroethane and which areespecially adapted for use as compression refrigerants particularly insystem using centrifugal or rotary compressors.

The refrigerant capacity per volume pumped of a refrigerant is largely afunction of boiling point, the lower boiling refrigerants generallyoffering the greater capacity at a given evaporator temperature. Thisfactor to a great extent influences the design of refrigerationequipment and aiects capacity, power requirements, size and cost of theunit. Another important factor related to boiling point of therefrigerant is minimum cooling temperature desired during therefrigeration cycle, the lower boiling refrigerants being used toachieve the lower refrigeration temperatures. For these reasons a largenumber of refrigerants of different boiling temperature and capacity arerequired to permit flexibility of design and the art is continuallyfaced with the problem of providing new refrigerants as the need arisesfor new capacities and types of installations.

The lower aliphatic hydrocarbons when substituted by uorine and chlorineare well-known to have potential as refrigerants. Many of theseuoro-chloro hydrocarbons exhibit certain desired properties includinglower toxicity and nonammability which have resulted in the extensiveuse of such components in a large number of refrigeration applications.Trichloroiluoromethane (CClaF) and dichlorodiuoromethane (CCIZFZ) aretwo of the most commonly available chlorine-uorine hydrocarbonrefrigerants available today. There is a recognized need for arefrigerant with a boiling point temperature between the relatively hightemperature of trichlorouoromethane -|-23.78 C. at atmospheric pressure,and the relatively low temperature of dichlorodiuoromethane, 29.8 C. atatmospheric pressure, in order to have available refrigerants of goodperformance and varying capacities.

Several nuoro-chloro hydrocarbons have boiling points in this range butsuffer from other deficiencies such as flammability, poor stability orpoor thermodynamic performance. Some examples of these types ofrefrigerants are tetrauorodichloroethane, uorodichloromethane,diuorochloroethane and uorochloromethane.

It would also be possible to achieve the desired boiling point by mixingtwo refrigerants with boiling points above and below the desired one. Inthis case, for example, mixtures of trichlorofluoromethane anddichlorodiiluoromethane could be used. It is well known, however, thatsimple mixtures create problems in design and operation because ofsegregation of the components in the liquid ICC and vapor phases. Thisproblem is particularly troublesome in systems using centrifugalcompression because of the large quantities of liquid usually found inthe evaporator.

An object of the present invention is to provide new mixtures with aboiling point between that of trichlorouoromethane anddichlorodiuoroethane suitable for use as a refrigerant. Moreparticularly it is an object of the present invention to provide arefrigerant system with a capacity between the refrigeration capacity oftrichlorouoromethane and dichlorodiiluoroethane and which is useful as acompression refrigerant, particularly in systems using a centrifugal orrotary cornpressor. Another object is to provide a new low boilingazeotropic mixtures which are useful in producing refrigeration in thosesystems in which cooling iS achieved by evaporation in the vicinity ofthe body to be cooled and in which because of the nature of the system,the problem of segregation is critical. A further object is to providelow boiling azeotropic mixtures in which the ammability is reduced tosubstantially negligible proportions.

The drawing shows boiling temperature of azeotropic mixtures accordingto the invention and will be discussed in more detail hereinafter.

In accordance with the invention it has been discovered thatcompositions consisting of dichlorotetra. uorocthane (C2Cl2F4) withapproximately 30 Weight percent to weight percentmonochloromonofluoromethane (CHZCIF) from azeotropic mixtures which haveboiling points of about 12 C. at atmospheric pressure.Monochloromonofluoromethane has a boiling point temperature of -9.6 C.and dichlorotetrauoroethane has a boiling point temperature of +3.6 C.,at atmospheric pressure. These monochloromonoiluoromethane anddchlorotetralluoroethane mixtures have a marked reduction in boilingpoint temperature as compared with the boiling temperature of thecomponents. From the properties of the components alone the markedreduction in the boiling point temperature and the azeotropiccharacteristics of the mixtures are not expected.

The indicated monochlorornonofluoromethane and dichlorotetraliuoroethanemixtures provide substantial increased refrigeration capacity over thecomponents and represent new refrigeration mixtures useful especially insystems using centrifugal and rotary compressors. The use of themonochloromonouoromethane and dichlorotetrauoroethane mixtures eliminatethe problem of segregation in handling and the operation of the systembecause azeotropic mixtures behave essentially as a single component ascompared to simple mixtures. Furthermore, flammability ofmonochloromonouoromethane is reduced by admixture withdichlorotetrafluoroethane such that all mixtures within the indicatedrange are substantially non-flammable.

An evaluation of the refrigeration properties of themonochloromonofluoromethane and dichlorotetrafluoroethane mixture andits components are shown in Table I, below.

It is particularly pointed out in relation to the data of Table I that(1) the compression ratio of the azeotrope is lower than eithercomponent, and this property allows more elicient compressor and design,and (2) the compressor displacement shows the displacement of azeotropeto be lower than either component, which is of obvious advantage in acompressor. In addition, its H.P./ton value is much superior to that ofdichlorotetrauoroethane. When operated on similar cycles mostrefrigerants have very similar H.P./ ton requirements. In centrifugalsystems even small differences in H.P. per ton are quite importantbecause of the large quantities of energy involved. Power cost is amajor item in the operating costs of such systems. A favorably low powerrequirement is thus of particular benefit in refrigerants forcentrifugal service. Furthermore, the mixture does not have the problemof flammability associated with pure monochloromonofluoromethane.

In addition, it is known that in the case of some refrigerants, such asdichlorotetrauoroethane, on isentropic compression, such as occurs inthe refrigeration cycle of a centrifugal or rotary compressor, thesaturated vapor will partially condense. This is an undersirablesituation as the liquid causes ineiciences and erosion in thecompressor. To overcome this wet compression the gas must be somewhatsuperheated before compression which requires heat exchange equipment.On the other hand, some refrigerants have a tendency to heat excessivelyon isentropic compression. This results in undersirable high temperaturein the system (monochloromonouoromethane and dichloromonofluoroethaneare examples of this type of refrigerant). Themonochloromonofluoromethanedichlorotetrafluoroethane mixtures, however,heat only slightly on compression and thus substantially avoid wetcompression as well as excessive heat on compression and thus areparticularly useful as refrigerant liquids.

Boiling points of monochloromonoiluoromethane anddichlorotetrauoroethane mixtures were determined usingmonochloromonoluoromethane and dichlorotetrafluoroethane compoents ofbetter than 99.9% purity. Monochloromonouoromethane anddichlorotetrailuoroethane mixtures of various compositions were preparedand boiling points were measured at about 45 p.s.i.a. by thermostattingthe mixture and varying the temperature until the vapor pressure reachedabout 45 p.s.i.a. Temperatures were measured using a platinum resistancethermometer.

TABLE 1I Boiling points of CH2ClF/C2C12F4 mixtures At about 45 p.s.i.a.

Weight percent CHZClF Boiling in solution: point C. 100.00 20.80 90.0019.57 80.02 18.73 70.04 18.16 65.00 17.99 58.60 17.86 55.12 17.84 50.0017.88 44.80 18.00 39.96 18.17 30.00 18.92 20.00 20.54

The data of Table Il is plotted in the drawing. This data shows thatmixtures at 45 p.s.i.a. of about 30 to 80 weight percentmonochloromonouoromethane have boiling points within about 1 C. andhence substantially similar vapor pressures. At 1 atmosphere the boilingpoints of these compositions are about 12 C. The compositions within therange of 45 to 65 weight percent monochloromonoluoromethane have boilingpoints within about 0.2" C. at 45 p.s.i.a. Because the temperature andhence the vapor pressures are so similar between the weight percentlimits set forth in the last sentence, those weight percent limits areespecially preferable.

As shown in the drawing, it has been found that the most preferablepercentage by weight monochloromonouoromethane component in themonochloromonouoromethane-dichlorotetrailuoroethane azeotropic mixtureis about 55 percent.

Makeup of the azeotropic mixture of the invention requires no specialprocedures. The monochloromonouoromethane-dichlorotetrauoroethanecomponents employed should be substantially pure, preferably at leastabout 99.0% pure, and contain no substances deleteriously effecting theboiling characteristics of the mixture or use as refrigerante.

The mixtures of the invention exhibit desired refrigeration properties,include non-flammability, boiling point substantially lower than eithercomponent, compression ratio lower than either component, lack of thepresence of wet compression, and superior H.P./ton value. In addition tobeing used as new refrigerants providing refrigeration, especially insystems using centrifugal or rotary compressors, it will be noted thatthe mixtures disclosed herein may also be used for other purposes,including a heat transfer medium, gaseous dielectric, or as a workingfluid in a power cycle.

It is intended that applicants scope of protection only be limited bythe claims that follow.

We claim:

1. A low boiling azeotropic composition consisting of a mixture ofmonochloromonouoromethane and dichlorotetraluoroethane in which theweight percent of monochloromonofluoromethane is within the range ofabout thirty to eighty.

2. A low boiling composition as recited in claim 1 said weight percentof monochloromonouoromethane being within the range of about forty-fiveto sixty-five.

3. A low boiling composition as recited in claim 2, said weight percentof monochloromonouoromethane being about ifty-ve.

4. The process of producing refrigeration which cornprises condensing anazeotropic mixture consisting of monochloromonouoromethane anddichlorotetrafluoroethane in which the Weight percent ofmonochloromonofluoromethane is within the range of thirty to eighty, andthereafter evaporating said mixture in the vicinity of a body to becooled.

S. The process of producing refrigeration recited in claim 4, saidweight percent of monochloromonouoromethane being within the range offorty-five to sixty-live.

6. The process of producing refrigeration recited in claim 5, saidweight percent of monochloromonofluoromethane being about iifty-iive.

References Cited UNITED STATES PATENTS 3,047,506 7/ 1962 Broadley 252-67FOREIGN PATENTS 529,031 11/ 1940 United Kingdom.

LEON D. ROSDOL, Primary Examiner S. D. SCHWARTZ, Assistant Examiner U.S.Cl. XR. 252-78; 62-112

